1. Field of the Invention
The present invention relates generally to the field of ophthalmic devices, more particularly to intraocular lenses (IOLs), and still more particularly to thin profile monofocal refractive IOLs for implanting in narrow ocular regions, especially the anterior chamber of an eye.
2. Background Discussion
The following definitions are considered helpful to the understanding of the present invention:
The term xe2x80x9cphakicxe2x80x9d applies to an eye in which the natural crystalline lens is still present.
The term xe2x80x9caphakicxe2x80x9d applies to an eye from which the natural crystalline lens has been surgically removed, for example, due to the formation of cataracts on the lens.
The anterior chamber of an eye is the narrow region between the back, endothelial surface of the cornea and the front surface of the iris.
The posterior chamber of a phakic eye is the narrow region between the back surface of the iris and the front surface of the natural crystalline lens.
A Fresnel lens (as defined at page 167 of the DICTIONARY OF OPTICS, published by Butterworth Heinemann, 1995) is xe2x80x9cA lens surface of narrow concentric rings or prism sections of a specified power that gives the effect of a continuous lens surface with the same power, but without the usual thickness and weight.xe2x80x9d
Glare (as defined at page 53 of THE GLOSSARY OF OPTICAL TERMINOLOGY, published by Professional Press Books, Fairchild Publications, 1986) is xe2x80x9cAny degree of light falling on the retina in excess of that which enables one to see clearly.xe2x80x9d And alternatively as xe2x80x9cAny excess of light which hinders rather than helps vision. (Too much light in the wrong place.)xe2x80x9d
Vision in a phakic eye is caused by light from a viewed object being refracted by the cornea and the natural crystalline lens to form an image on the retina at the back of the eye. Corrective spectacles, contact lens or corneal reshaping may be used to assist such image formations Optical muscles connected to a normal crystalline lens change the shape of the lens as needed to provide images of objects at different distances from the eye, an optical process known as accommodation.
The prevailing procedure for restoring vision (except for accommodation) in an aphakic eye is the surgical implanting of a refractive artificial lens, called an intraocular lens (IOL), ordinarily in the capsular bag from which the natural lens has been removed.
In addition to continued development of IOLs for restoring vision in aphakic eyes, considerable attention has recently been directed toward developing refractive IOLs (and insertion instruments) for implanting in the anterior chamber of phakic eyes having normal crystalline lenses to correct such vision defects as myopia, hypermetropia, presbyopia and astigmatism. The implanting of such corrective IOLs can potentially eliminate the wearing of spectacles or contact lenses, and/or eliminate permanent surgical procedures involving the cornea.
Anterior chamber-type IOLs may alternatively be implanted in posterior chambers of phakic eyes for providing corrective power to the natural lens, as may be needed due to subsequent physiological changes of the natural lens as an individual ages.
The anterior chamber is generally dome-shaped and very narrowxe2x80x94typically only about 3 mm at its center. The posterior chamber of a phakic eye be even more narrow, depending upon the size of the crystalline lens and the amount of its accommodation the width of the posterior chamber of a phakic eyexe2x80x94the successful implanting of a corrective IOL in either of these ocular chambers is extremely difficult and risks injuring delicate ocular tissue, especially the cornea""s endothelial surface in the case of anterior chamber implanting. Consequently, refractive corrective IOLs, particularly the IOL optics, are desirably made as thin as possible consistent with providing the requisite corrective power and structural stability of the optic.
To this end, several known patents disclose the use of a Fresnel lens on one surface of a refractive IOL optic. For example, U.S. Pat. No. 4,673,406 to Schiegel (issued Jun. 16, 1987) discloses a one-piece foldable refractive IOL with one surface of its central lens body formed as a Fresnel lens to reduce the thickness of the optic to enable the IOL to be implanted in a folded condition into an eye through a small corneal incision. The patent further discloses that individual zones of the multi-zone Fresnel lens are selected such that the focal points of all the zones coincide so as to reduce spherical aberration.
As another example, U.S. Pat. No. 4,787,903 to Grendahl (issued Nov. 29, 1988) discloses a refractive IOL or corneal lens having an optic that incorporates a Fresnel lens with multiple, concentric ring-zones. The Grendahl lens is further disclosed as being made of a composite material that allows refractive index modification with electromagnetic energy. (The Grendahl patent asserts a first use of a Fresnel lens for IOLs or corneal lenses, the Grendahl patent application having been filed shortly before the Schiegel patent application was filed).
As still further examples, U.S. Pat. No. 4,846,833 to Cumming (issued Jul. 11, 1989) discloses the forming of a Fresnel lens on the back surface of a posterior chamber IOL so the Fresnel surface will be sealed by the posterior capsule surface upon the implanting of the IOL in an aphakic eye. U.S. Pat. No. 6,096,077 to Callahan et al. (issued Aug. 1, 2000) discloses a thin IOL having the posterior surface formed of a stepped series of annular concentric rings of increasing diameter surrounding a central planar disc region; although, the Callahan et al. patent does not specifically identify the IOL posterior surface as being a Fresnel lens, the associated figures indicate that such is the case.
A characteristic common to the four above-cited patents is that the Fresnel zones comprise a series of staircase-like concentric zones separated from one another by abrupt transition steps. None of the Specifications of the cited patents describe these transition steps, however the accompanying figures depict the transition steps as having flat transition surfaces that are parallel to one another and to the optical axis of the optic, as are all Fresnel lenses. Moreover, none of the above-cited patents disclose any glare effects that may be caused by the flat transition steps between Fresnel zones.
As shown below by the present inventor, IOLs having abrupt Fresnel zone transition steps with flat surfaces induce substantial distracting and potentially hazardous glare in the IOL wearer""s eye when light (especially bright light) impinges on the lens optic as, for example, is commonly encountered in night driving or when driving into the sun.
Accordingly, a principal objective of the present invention is to provide a narrow profile (that is, thin) IOL, in particular, a narrow profile monofocal IOL that substantially minimizes such visual glare problems.
In accordance with the present invention, a narrow profile, glare reducing refractive monofocal intraocular lens comprises an optic having an anterior surface and a posterior surface and an optical axis. One of the anterior and posterior surfaces is formed having adjacent first and second peri-axial, stepped imaging zones, the second peri-axial imaging zone having the substantially the same optical power as the first peri-optical imaging zone.
A transition zone between the first and second peri-axial imaging zones is preferably formed having a surface of continuous variable curvature so as to reduce both indirect glare (caused by refraction) and direct glare (caused by diffraction) in an individual""s eye in which the intraocular lens is implanted from light impinging on the optic.
Positioning means are joined to the optic for positioning the intraocular lens in the eye with the optical axis of the optic generally aligned with the optical axis of the eye.
The first peri-axial imaging zone may be circular in shape and be centered at the optical axis of the optic and may have a diameter between about 4.3 mm and about 4.5 mm. The second peri-axial imaging zone is in such case formed in annular ring around the first peri-axial imaging zone.
The first peri-axial imaging zone may be recessed in the optic relative to the second peri-axial imaging zone. Alternatively, the second peri-axial imaging zone may be recessed in the optic relative to the first peri-axial imaging zone.
In combination, the first and second peri-axial imaging zones and the transition zone define one surface, preferably the posterior surface, of the optic that has a preferred maximum thickness at any point of between about 0.30 mm and about 0.40 mm. Also the optical power of the peri-axial transition zones is preferably outside the diopter range of about xe2x88x925 to about +5.
Still preferably, the height of the transition zone, the surface of which may be generally S-shaped, is preferably between about 0.10 mm and about 0.40 mm and the width of the transition zone is preferably between about 0.15 mm and about 0.30 mm.
In one variation intraocular lens, the transition zone surface has a continuous curvature that eliminates glare caused by diffraction and in another variation intraocular lens the transition zone has a surface of variable curvature that that reduces glare caused by refraction.